Layer coating systems, particularly those formed by the sputter coating process are well known in the architectural and automotive field. Such coatings for solar management purposes seek to achieve among other characteristics, the recuisite reflection of infrared energy and at the same time, the requisite amount of transmittance of visible light. In the automotive windshield art, for example, the windshield normally must have a visible light transmittance of no less than 70% even when laminated. The need for high infrared reflectance and high visible transmittance often conflict with each other. Making the design of an appropriate, commercial layer system even more difficult is the further need to achieve a desirable (usually substantially neutral) color, and/or low visible reflectivity (i.e., a non-mirror like appearance). Adding still further to the problems faced in the art in achieving a commercially acceptable product is either the need or desirability of forming a layer system which is heat treatable (i.e. well not deteriorate when going through a heat treatment such as bending, tempering or heat strengthening).
Design criteria for such systems do not normally focus alone on sea treatability and/or solar management characteristics as described above. Rather, a major problem that has often faced the I.G. unit and automotive windshield art after an otherwise acceptable sputter-coated layer system has been developed from a solar management and heat treatability perspective, is the need to achieve mechanical durability. This is due to the fact that after the layer system is deposited, the intermediate product so produced usually requires mechanical handling to place it in its final form. Such handling steps are often of such a nature, in this respect, that the layer coating must be contacted by hand or by some mechanical device, and thus subject to abrasion. If the coating does not have sufficient “mechanical durability,” numerous rejects caused by scratching, particle abrasion, etc. are likely to occur during the manufacturing process.
Such a problem is particularly acute in the laminated (vehicular) windshield and the insulating glass unit (I.G. unit) arts. In these arts, it is to be noted, the layer system need not always be truly “chemically durable” since the layer is usually not exposed to weather because it is located between the laminated glass sheets in the windshield or between the two or more glass sheets in an I.G. unit. In other instances, however, where chemicals are to come into contact with the layer system during or after the manufacturing process, chemical durability is also desirable to achieve.
To demonstrate the need for mechanical durability, a typical manufacturing process for a conventional laminated front, bent automobile windshield may be referenced. In such a process, after jumbo sheets are cut from glass coming from the float process and then sputter coated with the layer system of choice, steps such as washing with revolving brushes, placement of the sheets in shipping racks, further cutting to particular sizes and washing, are typical preliminary steps which contain procedures that can mechanically harm the coating if it is not sufficiently durable.
Thereafter, in the making of a typical laminated windshield, numerous procedures are engaged in which require such potentially mechanically damaging steps as suction cup lifting, edge grinding, racking for shipment, flipping, separation using particles of diatomaceous earth and the like. Thereafter, the two sheets must be slumped together in a furnace to achieve their laminated shape (thus requiring heat treatability) The glass sheets must then be separated, the vinyl polymer safety sheet inserted (where a potential for scratching occurs) and, then, finally the sheets placed back together again and pressed together (with the aforesaid particles of diatomaceous earth often still therebetween with their potential for abrasive scratching) to form the windshield product. The need for a highly durable layer coating system in such a product is self evident and its achievement is a known problem, as aforesaid, in the art
In commonly owned U.S. Pat. No. 5,557,462 (having overlapping inventorship herewith) there is disclosed a dual silver, low-E layer coating system useful in I.G. units. In the preferred embodiments mechanical durability was found to be quite acceptable even in the manufacture of I.G. units which, as aforesaid, requires potentially damaging handling steps. The preferred systems of this '462 invention were also chemically durable. In addition, emissivity values were quite low, as was reflectance. Color was also in the acceptable range. However, the systems disclosed were not heat treatable and thus could not realistically be used where bent windshields were involved, or other heat treatments such as tempering or heat strengthening or glass welding were later contemplated.
In commonly owned U.S. Pat. No. 5,688,585 (having overlapping inventorship herewith) matchable, heat treatable layer systems are disclosed which are highly durable and chemically resist. The systems contemplated, however, are non-silver containing and thus could not avail themselves of the advantages of silver in achieving certain solar management properties, particularly infrared energy reflection, for which silver is commonly used in the sputter coating art. Moreover, while achieving high durability, visible transmittance values, in practice, in certain systems both before and after heat treatment, were less than about 70%. Such systems could, therefore, not be used as windshields. Moreover, due perhaps to the lack of silver, emissivity values while considered “low-E” were, in fact, in the relatively high range for such infrared reflecting glass products.
In another known layer system which is prior art to our invention, there is presented a dual silver system which comprises from the glass substrate outwardly (and which has approximately the following layer thicknesses):
STD ILayerThickness (Å)Si3N4 and/or TiOx (possibly)(125)ZnO(380)TiOx(10-40)Ag(140-160)ZnOSi3N4ZnO(800)Si3N4ZnOTiOx(10-40)Ag(120)ZnO(360)Glass Substrate
This system is heat treatable but loses mechanical durability upon heat treatment and generally demonstrates poor chemical durability.
In still another known system, a heat treatable system is presented which is exemplified by the following commercialized structure (the top three layers apparently being optional):
STD IILayerThickness (Å)ZnSnOx (50-100)TiOx (possibly) (25)ZnSnOx(350)TiOx(10-50)Ag(140)ZnSnOx(900)TiOx(10-50)Ag(110)ZnSnOx(360)Glass
Our testing has demonstrated that this layer system lacks mechanical durability both before and after heat treatment as the term “mechanical durability” is defined herein.
Another known product which exhibits a lack of durability consists of a repetitive three membered layer structure of ZnO/SnOx/ZnO which sandwiches two layers of silver. Other layer systems in generally this and the above-described generic category are found in U.S. Pat. Nos. 4,413,877; 4,898,789; 4,898,790 and 4,806,220.
In view of the above it is apparent that there exists a need in the art for a layer coating system useful in laminated windshields, I.G. units and other coated glass produces which is highly durable, and preferably is also, heat treatable, has significantly low-E qualities, and, in certain embodiments, manifests high visible transmittances sufficient for the automotive windshield art. It is a purpose of this invention to fulfill this and other needs in the art which will become more apparent once given the following disclosure.